Lithium Iron Phosphate Glasses Research Articles

Governing mechanism of ion transport in lithium-iron-phosphate glasses

We show a fundamental relationship between network structural attributes and ionic transport of lithium iron phosphate glasses xLi2O–2Fe2O3–3 P2O5 (xLFPO; x = 0.375, 0.75, 1.5, 3.0) used for a cathode in lithium-ion batteries. The glass samples have been synthesized using a solid-state reaction method. We have investigated the electrical characteristics of the glass by combinational measurements of electrical impedance in the frequency 100 Hz – 30 MHz and temperature from ambient to 240 °C, differential thermal analysis, X-ray diffraction pattern, and Raman spectroscopy. The ionic hopping and relaxation processes in xLFPO glasses are analyzed by using Cole-Cole, power law, and modulus representations. We reveal that the exponential increase in dc conductivity with increasing Li2O in xLFPO glasses is caused by the combination of an increase in non-bridging oxygen sites and a change in the bonding forces of iron valence surrounding the iron phosphate clusters inside the network. The power law conductivity, which is driven by the fractional Rayleigh equation, exhibits that the rate of increase in dc ionic conductivity is the same as the rate of increasing numbers of the ionic charge carriers. Raman spectra show that the increase of depolymerization of the iron phosphate network with the addition of Li2O content is due to the conversion of Q2 to Q1 and Q0 species.

Enhanced surface crystallization of glass by adding traditional oxide nucleating agents

Abstract In the preparation of glass–ceramics, bulk crystallization of glasses can be improved by adding nucleating agents. However, surface crystallization of glasses conventionally can only be enhanced by using small particles, whose surfaces provide nucleating sites. Herein, oxide nucleating agents such as TiO 2 and Cr 2 O 3 which are normally used to improve bulk crystallization were introduced into a lithium–iron-phosphate (LIP) glass. Differential thermal analysis results suggest that tendency to bulk crystallization of the LIP glass increases to some extent after addition of the nucleating agents. However, no bulk crystallization really occurred in the thermally treated samples. Instead, surface crystallization of the glass is facilitated by the nucleating agents. The samples containing nucleating agents show thicker crystallized surface layers compared with the pure LIP glass. It is proved nucleation stage to be important to increase the surface crystallization, further confirming the enhancement effect of the nucleating agents on surface crystallization. The results enrich the understanding of surface crystallization of glass and provide useful information for the preparation of glass–ceramics via glass powder sintering process which is based on surface crystallization.

Influence of Alumina Additions on the Physical and Chemical Properties of Lithium-iron-phosphate Glasses

Abstract Alumina improves the properties and depresses the devitrification of soda-lime-silicate glasses. Herein, the influence of alumina on the glass transition temperature, density, chemical durability, crystallization of lithium-iron-phosphate (LIP) glass has been investigated. As alumina was added to replace the iron oxide in a base LIP glass with the molar composition of Li 2 O:Fe 2 O 3 :P 2 O 5 =30:20:50, the alumina-containing glasses have increased T g , densities and chemical stabilities than the base glass. When the amount of alumina is increased from 2 to 6 mol, the T g value slightly increases, whereas the density decreases. However, the smallest weight loss is shown for the glass containing 3.2 mol of alumina. The variations of the properties with alumina are explained based on the infrared structure analysis results. In addition, it is found the either the base or the alumina-containing glasses have surface crystallization upon heat-treatments. Under the same treatment conditions, the base glass exhibits a thin layer of crystallization with LiFeP 2 O 7 as the main phase. In contrast, alumina-containing glasses show much higher degree of crystallization, which is further increased with the amount of alumina. This trend is opposite to that of silicate glass. Besides the LiFeP 2 O 7 main phase, Fe 7 (PO 4 ) phase is also identified in the crystallized alumina-containing glasses.

Formation mechanism of LiFePO<sub>4</sub> in crystallization of lithium iron phosphate glass particles

Formation mechanism of LiFePO<sub>4</sub> in crystallization of lithium iron phosphate glass particles

Structure and properties of ZnO-containing lithium–iron–phosphate glasses

Lithium–iron–phosphate glasses with compositions of (20 − x)Li 2O· xZnO·30Fe 2O 3·50P 2O 5 ( x = 0–7.2) have been prepared. The influences of the amount of ZnO on the structure, physical and chemical properties, and crystallization behavior of the glasses were investigated using Fourier transform infrared spectroscopy, differential thermal analysis and X-ray diffraction techniques. The density of glass was measured according to the Archimedes principle. The chemical stability was evaluated based on the weight loss after the glass particles were boiled in water. The results indicate that Zn 2+ ions cross-linked the phosphate chains by forming P–O–Zn bridges when 2 mol% of ZnO was added. When the amount of ZnO was further increased, [ZnO 4] tetrahedra were formed and ZnO acted as a glass network former, integrating the phosphate glass network. The density, chemical stability and the activation energy of crystallization of the glasses increased with the amount of ZnO, whereas the glass transition temperature decreased. All thermally treated glasses showed surface crystallization with LiFeP 2O 7 as the crystalline phase.

Crystallization Behavior of Lithium–Iron-Phosphate Glasses with Additions of ZrO2

Lithium–iron-phosphate (LIP) glasses with different amounts of zirconia were prepared by conventional melting and annealing process. The influence of the nucleation agent, zirconia, on the crystallization behavior of LIP glasses has been studied using differential thermal analysis (DTA), X-ray diffraction (XRD) and scanning electronic microscopy (SEM) techniques. The results show that addition of 2 wt% of zirconia results in increases in the glass transition and crystallization temperatures and a decrease in the activation energy of crystallization. However, both temperatures decrease with increased addition of zirconia while the activation energy increases. The zirconia-free LIP glass only shows surface crystallization with crystals of LiFeP2O7. The glass containing 2 wt% of zirconia also has surface crystallization; however, mixed ZrP2O7 and LiFeP2O7 are crystallized. The addition of 5 and 8 wt% of zirconia leads to bulk crystallization and increasing formation of ZrP2O7 crystals besides the LiFeP2O7 phase.

Crystallization Behavior of Lithium Iron Phosphate Glass Powders in Different Atmospheres

Crystallization behavior in different atmospheres (air, Ar, and 7% H2/Ar) of lithium iron phosphate glass (33Li2O–33Fe2O3–1Nb2O5–33P2O5 (LFNP)) powders with different sizes of 2–1000 μm was examined. The crystallization peak temperature (Tp) in Ar and 7% H2/Ar decreased with decreasing the particle size of glass powders, but the value of Tp in air was independent of particle size. The crystallized glass obtained by heating to Tp showed the formation of the α‐Li3Fe2(PO4)3 and LiFePO4 crystalline phases. Fe2O3 crystals were formed only in the inside of crystallized glass plates in the heating in air. The crystallization of LiFePO4 was largely enhanced in the particle size of <2 μm during the heating in Ar and 7% H2/Ar atmospheres. The main crystallization mechanism in LFNP glass was found to be surface crystallization. Significant shrinkages were observed for glass compacts (pellets) in the heating in 7% H2/Ar. These results suggest that controlling particle sizes and atmospheres enables the design the morphology of LiFePO4 crystals in LFNP glass.

Influence of alkali and alkali-earth metal oxide substitutions on the properties of lithium–iron–phosphate glasses

The influences of different alkali and alkali-earth oxide substitutions on the properties of lithium–iron–phosphate (LIP) glasses have been studied. Na 2O, K 2O, MgO, CaO and BaO were used to substitute Li 2O to prepare LIP glasses with molar compositions of (20 − x)Li 2O − xR 2O(RO) − 30Fe 2O 3 − 50P 2O 5 ( x = 2.4, 4, 5.6 and 7.2). The glass transition temperature ( T g ) was determined by the differential thermal analysis technique. The density and chemical durability of the prepared glasses were measured based on the Archimedes principle and the weight losses after the glasses were boiled in water. The results show that T g decreases with the initial substitutions, whereas the density and chemical durability increase. The diminution of the aggregation effect of Li + ions on the glass structure due to the decrease in Li + concentration, the larger molecule weights of the substitutes, the mixed-alkali and depressing effects as well the slower mobility of substitute ions mainly contribute to the initial changes in T g , density and chemical durability of the LIP glasses, respectively. Further increasing the amounts of substitutes brings about increasing diminution of the aggregation effect of Li + ions and breakage of the glass network on the one hand and increasing amounts of substitutes with larger molecule weights and ion radii on the other hand. Both aspects influence the glass properties oppositely and consequently non-monotonic variations in the properties of LIP glasses with the substitutions are observed.

Studies on glass transition of lithium-iron phosphate glasses

Abstract Amorphous analogs of lithium-iron phosphates (LFP) were prepared by standard press-quenching method and their thermal stabilities as well as structural properties were studied for the first time. Glass transition temperature T g determined by DTA method was observed at the temperature range 492–523°C, depending on the glass composition. The maxima of crystallization peaks were observed in the 555–579°C range. In products obtained after heating up to 700°C the XRD patterns have revealed the presence of: LiFePO4 (triphylite), FePO4 (heterosite), α-FePO4 (quartz like structure) and Li3Fe2(PO4)3 (Nasicon like structure) phases.

Lithium ion conductive glass–ceramics with Li 3Fe 2(PO 4) 3 and YAG laser-induced local crystallization in lithium iron phosphate glasses

The glasses with the composition of 37.5Li 2O–(25 − x)Fe 2O 3– xNb 2O 5–37.5P 2O 5 (mol%) ( x = 5,10,15) are prepared, and it is found that the addition of Nb 2O 5 is effective for the glass formation in the lithium iron phosphate system. The glass–ceramics consisting of Nasicon-type Li 3Fe 2(PO 4) 3 crystals with an orthorhombic structure are developed through conventional crystallization in an electric furnace, showing electrical conductivities of 3 × 10 − 6 Scm − 1 at room temperature and the activation energies of 0.48 eV ( x = 5) and 0.51 eV ( x = 10) for Li + ion conduction in the temperature range of 30–200 °C. A continuous wave Nd:YAG laser (wavelength: 1064 nm) with powers of 0.14–0.30 W and a scanning speed of 10 μm/s is irradiated onto the surface of the glasses, and the formation of Li 3Fe 2(PO 4) 3 crystals is confirmed from XRD analyses and micro-Raman scattering spectra. The crystallization of the precursor glasses is considered as new route for the fabrication of Li 3Fe 2(PO 4) 3 crystals being candidates for use as electrolyte materials in lithium ion secondary batteries.

Mössbauer analysis of Fe ion state in lithium iron phosphate glasses and their glass-ceramics with olivine-type LiFePO 4 crystals

The valence and local coordination state of Fe ions in 26Li 2O–43FeO–5Nb 2O 5–26P 2O 5 (mol%) glasses and glass-ceramics consisting of LiFePO 4 crystals (a potential candidate as cathode materials for rechargeable lithium ion batteries) are studied from Fe 57 Mössbauer effect spectrum measurements. The main valence of Fe ions in the precursor and crystallized glasses is found to be Fe 2+ (more than 80%). Fe 2+ ions in the precursor glasses give the values of the isomer shift δ = 1.16 – 1.19 mm / s and the quadrupole splitting Δ = 2.26 – 2.40 mm / s , indicating the presence of FeO 6 octahedra. Olivine-type LiFePO 4 crystals in the crystallized glasses show the values of δ = 1.22 mm / s and Δ = 2.94 – 2.96 mm / s , demonstrating that Fe 2+ sites in LiFePO 4 crystals are highly distorted octahedra. The presence of Fe 3+ ions with octahedral and/or tetrahedral local structures are suggested in the precursor glasses. It is proposed that similarities in the valence and local coordination state of Fe 2+ in the precursor glasses and LiFePO 4 crystals would be one of the reasons why LiFePO 4 crystals are easily formed through the crystallization of lithium iron phosphate glasses.

DTA, FTIR and impedance spectroscopy studies on lithium–iron–phosphate glasses with olivine-like local structure

Amorphous analogs of lithium–iron–phosphates (LFP) with olivine-like local order were prepared by standard press-quenching method and their thermal stabilities as well as structural and electric properties were studied for the first time. Glass transition temperature T g determined by DTA method is equal to 492–523 °C depending on the glass composition. Fourier transform infrared (FTIR) absorption spectroscopy was used to study local order. Local structure and thermal properties are almost independent on the lithium content. Electrical properties were studied by impedance spectroscopy. Impedance measurements indicated that the studied lithium–iron–phosphate glasses with olivine-like local order exhibit predominantly electronic (polaronic) conductivity. Total electrical conductivity at 450 °C for a glass of nominal composition LiFePO 4 approaches 10 − 2 S/cm. Electrical conductivity at 25 °C of Li 0.4FePO 4 glass after nanocrystallization (caused by heating up from room temperature to the beginning of crystallization temperature) increased by a factor close to 4. Nanocrystallization seems to be the way for electrical conductivity improvement of olivine-like cathode materials.